The problems associated with ink jet start-up are legion and notorious. Start-up problems include: (1) misfiring or non-firing of the initial ink droplets; and (2) slower initial ink droplet velocities.
Poor start-up is generally believed to be a result of evaporation of the ink in the nozzle of the ink jet during an idle period between firings.
Heretofore, such problems have been always addressed in a mechanical or electrical sense, i.e. added pulses or signals were used to discharge the initial drop of ink in order to prevent misfiring, and to accelerate the ink drop to normal operating speed.
To the best of our knowledge and belief, no one has ever tried to formulate an ink which would prevent or substantially reduce start-up problems.
To the best of our knowledge and belief, no one has ever realized that a blending of ink fluid components could eleviate problems associated with ink jet start-up.
The present invention was discovered quite by accident during the scientific and engineering research of formulating ink jet compositions using oleic acid, as taught in our U.S. patent application Ser. No. 248,551 filed: Mar. 27, 1981; now U.S. Pat. No. 4,361,843.
During the aforementioned research, it was noted that one particular formulation always started properly during initial discharge of the ink jet. This formulation comprised by approximate weight: 30 percent oleic acid; 20 percent Typophor Black (30% weight of Nigrosine and 70% weight of oleic acid); and 50 percent benzyl ether.
Analysis of this formulation revealed that the oleic acid and benzyl ether had similar boiling points and low vapour pressures. It was then decided to formulate other ink compositions with components having matching boiling points and/or vapour pressures to see whether they too would exhibit a freedom from start-up problems. It was indeed observed that these new compositions were also free from start-up problems.
The chemistry is not yet fully understood regarding all the parameters which enter into the method of blending ink components to reduce start-up problems. Other factors, such as viscosity, may play a part in properly matching ink fluid components. At this time, however, it is safe to state that the matching of vapour pressures and/or boiling points of the components reduces to a significant degree the aforesaid problem.
It is believed that the matching of vapour pressure and/or boiling points produces an ink whose components evaporate at substantially similar or equal rates, thus providing an ink that maintains its initial formulation percentages despite evaporation. It is believed that this phenomenon results in the elimination of the problems associated with start-up.
It should also be obvious in view of the above discovery, that components having a lower vapour pressure, such as oleic acid, would be most desirable for use in the invention.